This invention relates generally to valves and more particularly to gate valves which may or may not be positioned in a submerged operating condition and which gate valves may be controlled by a remotely energized valve actuator for inducing controlling movement to the gate of the valve. Such valves and valve actuators are frequently utilized in service conditions where the valve is physically located remote from the control and monitoring facility as, for example, when wellhead valves are positioned on the ocean floor and controlled from a platform or from a shore based control facility. When such valves are utilized on remotely located wellheads, it is necessary to know when the valve element is in the fully open or fully closed position in each of the various valves to determine their operative condition and to assure proper control. For this purpose, electrical signals have been used to relay information to the control facility regarding the position of the valve element. In the event an erroneous signal is sent to the control and monitoring facility falsely indicating the position of a wellhead valve, severe damage or even destruction of the wellhead may be caused. Erroneous signals can be generated if the signal is made responsive to the movement of the controlling hydraulic fluid or is made responsive to physical movement of the valve stem or other of the hydraulic operator parts rather than the valve element itself. It is also possible that the gate structure may become disconnected from the valve stem or that some other malfunction may take place within the valve operator such that an erroneous signal is caused to be sent to the monitoring facility.
Most valve and valve operator signal indicator mechanisms rely on movement of hydraulic fluid or upon mechanically or hydraulically energized positioned indicator mechanisms which are related to the valve operator system rather than to the actual position of the gate member of the valve. The results produced by signal indicator systems of this type would not prevent an erroneous position signal from being sent to the monitoring facility in the event the gate becomes disconnected from the valve stem, for example, as sometimes occurs.
U.S. Pat. No. 3,538,948 discloses a gate valve having a gate position indicator which includes reed switches located in the valve chamber and actuated by permanent magnets carried by the valve element to energize an electrical circuit to effect transmission of an electrical signal indicating the position of the gate. In this particular gate valve, it is necessary to employ a protective sleeve to protect the reed switches from flowline fluids which enter the valve chamber. However, in subsea applications, the protective sleeve is susceptible to invasion by salt water whenever a large pressure differential exists between inside the valve housing and outside as occurs at great depths. Thus, pressure differential inside and outside the valve housing limits the depth at which this type of valve can safely be used. Also, the reliability of the indicator mechanism is diminished by the use of reed switches which include moving parts.
Accordingly, an object of the invention is to provide a valve having an internal position indicating means for signalling valve position to a remote monitoring facility which can be used in subsea applications at greater depths than has heretofore been achieved.
A further object is to provide a valve having an internal valve position indicating mechanism with electrical circuit means for electrically signalling valve position to a remote monitoring facility and with improved reliability of the signalling means and position indicating mechanism.
It is a still further object of the invention to provide a valve for subsea applications with a position indicating means responsive to valve element position for transmitting an electrical signal indicative of valve element position and which is also provided with means which are accessible to a diver whereby actual valve element position can be visually determined.
Other objects, advantages and novel features of the invention will be apparent to those of ordinary skills in the art upon examination of the following detailed description of a preferred embodiment of the invention and the accompanying drawings.